Sound transmission



June 30, 1931. H. D. ARNoLD soUND TRANSMISSION Filed June 14, 1929' atented June 30, 1931 :UNITEDv STATES PATENT OFFICE HAROLDlD. ARNOLD, OF SUMMIT, NEW JERSEY, ASSIGNO'IR TOV BELL TELEPHONE LAB- Y OBATORIES, INCORPORATED, OF NEW YORK, Y., A CORPORATION OF NEW YORK common line.

SOUND TRANSMISSION Application med :rune 14,

Y This invention relates to speech transmission systems and more particularly to binaural circuits suitable for use in sound pic-` ture syst-ems.

Various schemesrfor obtaining such a dis-v tribution have been proposed heretofore. Some of them were of the so-called binaural type in which twopick-up transmitters, located one on each side of the sound scene, were associated over separate circuits directly, or indirectly by means of intermediate sound records, with two correspondingly placed loud speaking receivers In these systems two entirely separate channels are necessary from the transmitters to the receivers. Other systems-contemplated mov ing the loud speakers or selectively energizing certain speakers of a group'so that the sounds always appeared to come from the proper part of the scene but thesev had the disadvantage of requiring intricate mechanical devices orV commutators and considerable incidental wiring.

According to the present invention there are a number of pick-up transmitters variously located wth respectv to the original sound scene and a' number of loud speakers similarly disposed with respect to the scene of reproduction. Switching means common to the speakers 'is selectively operated over the single transmission system Vconnecting them with the original scene by means of voice*v operated relaysV associated with the transmitters.. In order thatV the necessary switching may be laccomplished without interruption of the reproduction, the currents representing speechor music pass through a suitable delay network but the signal currents pass directly from the relays to the When this scheme is used for sound pictures instead of directly in public address systems the recorder is energized from the common line so that the recordcon-l tains not only the currents representing speech but also the necessary signals for actu- 1929. seriaiNo. 370,794.

ating the switching mechanism during reproduction. Y

The invention may be clearly understoody in a notation of the detailed descriptionv of the circuits shown in the drawings wherein- Fig: 1 discloses the invention adapted for use in a public address system in such a way that the loud speakers reinforce the original speakers voices and Fig.v 2 shows how this v circuit may be modified to adapt the invention fo-r use in sound picture systems.

Referring to Fig. 1, 1 and 2 are pick-up transmitters preferably disposed on either side ofthe original stage and. 3 and 4 arevacuum tube amplifiers associated with the transmitters and with the common transmission line 5 through anti-resonant circuit 6 and delay circuit 7 Also associated with transmitters 1 and2 are amplier-rectifier devices 8 and 9 which supply rectified speechenergy to the polarizedrelays 10 and 11 respectively. Oscillators 12 and 13 generate signal currents of suitable frequencies which are impressed upon the line 5 at suitable times through amplifiers 14 and 15 and transformers 16` and 17. In the receiving circuit an amplifier 18 delivers Vthe transmitted Vcurrents representing speech or music to the hybri-d coil 21 and thence to the loud'speaking receivers 19 and 20, which are lproperly placed to reinforce orv reproduce the original sounds in a realistic manner. The receivers are normally short circuited, yas indicated, by polarizing relays 22 and 23 which may be energized at the desired times by amplifierrectiiiers 24 and 25 associated with the receiving amplifier V18 through resonant cir-' cuits 26 and 27. In accordance with the usual practice in communication circuits the hybrid coil is terminated by a suitable network N so that the switching of one receiver does not aifect the volume level of the other.

If then an actor in the vicinity of transmitter 1 begins to speak it is evident that the sensitive relay 10 will be operated immediately by rectified currents from the device 8 so that contact 28 is opened thereby permitting oscillator 12, which is generating a definite frequency f1 such as 3500 cycles, to supply current of this frequency to the line 5. This current Will be transmitted Without delay and, resonant circuit 26 being tuned to its frequency, it Will pass to the device 24 and operate the relay 22 thereby conditioning loud speaker 19 to reproduce the speech about to be transmitted. The delay circuit 7 is designed to retard the transmission of speech sufficiently to permit the foregoing operations to occur before the speech energy reaches the hybrid coil 21 so that even the first syllables of the speech Will be reproduced by the re- .ceiver 19. As is Well known in the art this de- 'lay need be only a very small part'of a second. The amplifier 4 being a unilateral device it is evident that the relay 11 cannot operate so that the receiverl 20 remains short circuited at contact 29. Also the anti-resonant circuit 6 is designed to suppress both the signaling frequencies such as 3500 cycles and 4000 cycles Without material effect on adjacent frequencies'so that the quality of the speech transmitted is substantially unimpaired. Qbviouslyfthen, the receivers 19 and 20fcannot beoperated inadvertently since the speech energy transmitted over the line 5 does not contain components/of the signal frequencies generated by oscillators 12 and 13.

The relay 10 will, of course, be held operated as long` as the actor adjacent transmitter 1 is speaking but Will be released each time he pauses thereby deenergizing loud speaker 19 by releasing relay 22. Similarly When a speaker in the neighborhood of transmitter 2 begins tok talk the loud speaker .20 will be energized and deenergized as soon as he has iinished.v If at any time both actors arespeaking, both loud speakers will be energized but as soon as one has finished the corresponding speaker Will be deenergized by its relay 22 or 23. rl-hese relays may be adjusted to remain operated during slight pauses in the conversation but preferably are permitted to release after avery short interval of silence to 'prevent possible misoperation when the speakers follow each other in close succession. `When the invention is applied to a sound picture system the transmission line 5 Will, of course, terminateas shown in Fig. 2 in a recording device 30 which Will engrave a record blank 31, the trace of 'which will contain both speech and signaling frequencies in proper sequence. In this figure the amplifiers, relays, etc. at the recording station in Fig. 1 are indicated collectively by 32. Similarly kthe apparatus at the receiving station is indicated by 33. The reproducer 34 Will reproduce from the record 31, or a suitable copy of this record, the speech and signal frequencies recorded so that the loud speakers Will be operated in the same manner; as described in connection with Fig. 1.

While the invention has Ibeen described with reference to a particular system it is obviousthat it'may be modified in various Ways, such as bythe use of additional microphones and loud speakers with their necessary associated circuits, Without departing from the scope of the invention as defined in the following claims.

Vhat is claimed is:

1. In a transmission system a plurality of variously located sound pick-up devices, a plurality of signaling means, a transmission line including means common to the devices for delaying currentsy of voice frequencies,

circuits for the signaling means independent of the delaying means, a plurality of receivers variously located to correspond to the pickup devices, and means responsive to the signaling means for selectively associating the receivers With the line.

2. In a transmission system,'aplurality of sound'pick-up devices, atransniission line including a delay circuit common to the -devices, receiving means associated- With the line, and means responsive to each of the pick-up devices for energizing 'the receivingv 4. In a transmission system, a plurality-of` sound pick-up devices and a plurality ofnor-V mally inoperative receivers, a single tr-ansmission circuit connecting the pick-up devices and the receivers, means responsive -to sounds picked up by one ofthe devicesfor impressing a characteristic signal on thejl-ine and means responsive to thesi-gnal for preparing` the corresponding receiver torespond to currents from the pick-up device. Y

- 5. In a binaural recording and reproducing system, means for making a record of sounds land* means for reproducing-fthe record, said first means comprising at least two sound pick-up devices,` a recorder, aline connectingthe devices to the recorder and means responsive to each device for impressing upon the recorder a characteristic signal and said reproducing means comprising a. reproducer, at least tvvo receivers, a line connecting the reproducer land receivers and Vmeans responsive to the reproduced characteristic signals for selectively conditioning lthe receivers for operation'.

6. The combination with a plurality of pick-up devices, a transmission line includingv a delay circuit and a circuit anti-resonant to predetermined signal frequencies and means' for impressing the signal frequencies on the line beyond said circuits in accord-V ance with the operation of the pick-up devices, of means for recording currents and means responsive to the reproduced currents including receivers corresponding to the pick-up devices and selectively opera-ted in accordance with the signal frequencies.

In Witness whereof, I hereunto subscribe my name this 13th day of June, 1929.

HAROLD D. ARNOLD. 

